Our overall goal is to study regulation of hepatitis B virus (HBV) gene expression and events in virus replication in human, animal model and cell culture systems and to investigate mechanisms whereby persistent infection with hepatitis B virus causes chronic liver disease and leads to development of primary hepatocellular carcinoma. Our basic premise is that HBV genetic elements and/or specific viral gene products (regulatory or structural) by virtue of their direct function or a separate effect on host cell gene expression cause pathophysiologic consequences leading to chronic liver disease and/or hepatocyte transformation. Our specific aims will be (1) to study changes in HBV gene expression and/or genome replication which occur during persistent viral infection and to relate these changes to abnormalities in the virus assembly/secretion mechanism, (2) to study molecular forms of HBV genomes accumulating in liver during persistent infection and how these molecular forms and their accumulation might relate to the mechanism of hepatic oncogenesis, (3) to study cis and trans acting regulatory elements in the HBV genome and how these elements control HBV gene expression, (4) to determine whether factors which modify the function of HBV regulatory elements in cell culture systems influence HBV gene expression in vivo, and (5) to study how the HBV genome, its regulatory elements or gene products might interact with, modify expression of, or work in concert with cellular oncogenes or growth factors to alter growth of liver and/or other cells in culture. Specific experiments will utilize valuable tissue samples from So. African blacks with liver cancer who show an apparent defect in the virus replication/assembly/secretion pathway as well as tissues from Greek patients with replicative vs. non-replicative infection, and will use molecular hybridization, cloning and immunologic methods to characterize HBV molecules, viral proteins and viral particles accumlating in these tissues. Other experiments will use plasmid expression vectors (CAT) and DNA transfection methods to study regulatory elements in the HBV genome, transgenic mice, containing all or part of the HBV genome in a form expressable in a liver tissue specific manner to study tissue specific regulation in an in vivo model and factors (such as glucocorticoids, interferon, hepatotoxins and chemical carcinogens) which might modify HBV gene expression, and cell culture systems to study the role of HBV and other genes in causing immortalization and/or further transformation of hepatocytes or other eukaryotic cells. By this multifaceted approach, using modern molecular and cellular methods, we hope to gain further understanding of the possible role of HBV in chronic liver disease and primary liver cancer.